This invention concerns peptidomimetic isoprenyl transferase inhibitor compounds useful in the treatment of human cancers.
Ras oncogenes are prevalent in over 20% of all human cancers. The compounds of the invention inhibit the posttranslational processing of ras proteins, thereby inhibiting ras protein function.
Ras proteins are present in all cell types, and are thought to take part in normal cellular signal transduction mechanisms. Ras mutations are thought to cause hyperproliferation of cells; mutated ras genes are known as oncogenes. In particular, ras oncogenes are found in approximately 30% of all lung cancer, 30% of all myeloid leukemia, 50% of all colorectal carcinoma, and 90% of all pancreatic carcinoma. Barbacid, M., Ann. Rev. Biochem., 56:779 (1987), Bos, J. L., Cancer Res. 49:4682 (1989). Examples of ras mutations are found in H-ras, K-ras, and N-ras.
Like other members of the superfamily of small GTP-hydrolyzing proteins, ras-encoded proteins, both normal and mutated, require post-translational processing for cell membrane association and biological activity. Maltese, W. A., FASEB Journal, 4:3319 (1990), Hancock, J. F. et aL, Cell, 57:1167 (1989).
The post-translational processing of ras proteins is signaled by a short carboxyl-terminus consensus sequence, known as the CAAX box. This sequence signals which of two isoprenyl groups, farnesyl or geranylgeranyl, is to be attached to ras proteins by cellular enzymes. A farnesyl group is a 15 carbon isoprenyl group, while a geranylgeranyl group is a 20 carbon isoprenyl group. Isoprenyl groups are multimers of isoprene, a 5 carbon compound. For farnesylated proteins, such as ras, lamin B, and xcex3-transducin, C is cysteine, A is an aliphatic amino acid, and X (the carboxyl-terminal amino acid) is methionine, serine, or glutamine. Geranylgeranylated proteins such as Rap, Rho and other small GTP-binding proteins, have similar CAAX sequences in which X is usually leucine, or occasionally is phenylalanine. In vivo, ras proteins are preferentially farnesylated.
Post-translational processing of the ras-encoded protein includes at least three steps. First, reaction with farnesyl pyrophosphate attaches a farnesyl group to the Cys residue on the sulfhydryl side chain. Second, a specific protease cleaves the three carboxy-terminal amino acids. Third, the carboxylic acid moiety of the now-terminal cysteine is methylated to a methyl ester. The farnesyl transferase enzyme (FTase) mediates the attachment of the farnesyl group to a protein. The geranylgeranyl transferase I enzyme (GGTase I) mediates the attachment of the geranylgeranyl group to a protein.
Post-translational processing, particularly farnesylation, of ras proteins is critical for in vivo ras protein function. Among other things, farnesylation of ras oncogene products is known to be essential for ras-induced cellular transformation. Cox, A. D. and Der, C. A. Critical Rev. in Oncogenesis, 3 (4) 365-400 (1992). Upstream of FTase, farnesylation of a ras protein can be inhibited by mevalonate synthesis inhibitors such as lovastatin or compactin, which are HMG-CoA reductase inhibitors. Direct inhibition of FTase by short peptides or peptide-like substrates has also been demonstrated. Since ras proteins mediate the transformation of normal cells to cancer cells in many human cancers, compounds which inhibit prenylation will, therefore, inhibit the growth of ras-related cancers. A group of such compounds and methods for their synthesis are described in U.S. Pat. No. 5,840,918, the disclosure of which is incorporated by reference herein in its entirety, particularly the disclosure from column 17 to column 30, and Examples 1 to 175. Other compounds are disclosed in international patent publication WO 98/38162A1, which is also incorporated by reference herein in its entirety.
This invention is directed to novel peptidomimetic isoprenyl transferase inhibitor compounds useful in the treatment of ras-associated human cancers. Ras-associated human cancers are those in which a mutated form of the ras gene product are commonly found, e.g., lung cancers, myeloid leukemia, colorectal carcinoma, pancreatic carcinoma, and the like. In particular, the invention is directed to compounds with the following formulas: 
The invention concerns the compounds themselves, the preparation of these compounds, and the in vitro and in vivo isoprenyl transferase activity of these compounds. Another aspect of the invention is directed to the clinical use of the compounds to decrease isoprenyl transferase activity in biological systems, and to the physiological consequences of inhibition of isoprenyl transferase. In particular, the invention is directed to methods of using the compounds to treat ras-associated human cancers.
The compounds of the invention may be used clinically to treat medical conditions where a decrease in isoprenyl transferase activity is beneficial. The compounds of the invention can be used to inhibit post-translational modification of oncogenic ras proteins by FTase, thereby down-regulating ras protein-stimulated cell proliferation. Accordingly, the invention is directed to the treatment of various forms of ras-associated cancer. Some compounds of the invention inhibit post-translational modification of ras proteins by the related GGTase I, which also results in down-regulation of ras protein function. Certain compounds of the invention are selective or specific for FTase and are preferred over compounds which are selective for GGTase I.
Further, compounds of the present invention may contain asymmetric carbon atoms and hence can exist as stereoisomers, both enantiomers and diastereomers. All stereoisomers and mixtures thereof are considered to fall within the scope of the present invention. The synthetic examples cited herein provide the most preferred isomer.
The invention is also directed to prodrugs and pharmaceutically acceptable salts of the compounds described, and to pharmaceutical compositions suitable for different routes of drug administration and which comprise a therapeutically effective amount of a described compound admixed with a pharmacologically acceptable carrier.
The compounds of the invention have been found to be surprisingly and unexpectedly superior inhibitors of in vivo isoprenylation, i.e., isoprenylation of proteins, particularly ras proteins, when contacted with intact cells, compared with other known isoprenyltransferase inhibitor compounds. Without being bound by theory, it is believed that the increased lipophilicity of the compounds of the invention relative to other similar compounds provides for greater in vivo activity due to greater cell permeation.
Definitions
The term xe2x80x9cprodrugxe2x80x9d as used herein refers to any compound that may have less intrinsic activity than the xe2x80x9cdrugxe2x80x9d but when administered to a biological system generates the xe2x80x9cdrugxe2x80x9d substance either as a result of spontaneous chemical reaction or by enzyme catalyzed or metabolic reaction. Reference is made to various prodrugs such as acyl esters, carbonates, and urethanes, included herein. The groups illustrated are exemplary, not exhaustive and one skilled in the art could prepare other known varieties of prodrugs. Such prodrugs of the compounds of the invention fall within the scope of the present invention.
The term xe2x80x9cpharmaceutically acceptable saltxe2x80x9d includes salts of the compounds of the invention derived from the combination of a compound of this invention and an organic or inorganic acid. The compounds of the invention are useful in both free base and salt form. In practice the use of salt form amounts to use of base form; both forms are within the scope of the present invention.
The terms xe2x80x9ctreatmentxe2x80x9d or xe2x80x9ctreatingxe2x80x9d include prophylactic or therapeutic administration of compounds of the invention, for the cure or amelioration of disease or symptoms associated with disease, and includes any benefits obtained or derived from the administration of the described compounds.
Further, compounds of the present invention may contain asymmetric carbon atoms and hence can exist as stereoisomers, both enantiomers and diastereomers. All stereoisomers and mixtures thereof are considered to fall within the scope of the present invention. The synthetic examples cited herein provide the most preferred isomer.